Halogenated copolycarbonate end capped with trihalophenol

ABSTRACT

Disclosed is a novel polycarbonate which has 
     (1) a repeating unit (I) represented by the general formula: ##STR1##  and a repeating unit (II) represented by the formula: ##STR2##  (All the symbols are as defined in the claims); (2) a trihalogenophenoxy group as the end group thereof; and (3) a viscosity average molecular weight of 10,000 to 50,000 and 1 to 10 mol % of the repeating unit (I) in the main chain. 
     The polycarbonate is excellent in all of flame retardance, impact resistance, and a thermostability at molding. Accordingly, the polycarbonate of the present invention is extensively and effectively used as various industrial materials such as home electric appliances, office automation devices, construction materials and the like.

This application is a continuation-in-part, of application Ser. No. 07/585,739, filed Sep. 20, 1990, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel polycarbonate, more particularly, to a novel polycarbonate which is excellent in flame retardance, impact resistance, and thermostability at molding.

2. Description of the Related Arts

As halogen-containing polycarbonate copolymers having flame retardnace, various ones have heretofore been known. They include (i) a copolymer of tetrabromobisphenol A (TBA) and bisphenol A (BPA) (Japanese Patent Publication No. 24660/1972), (ii) a copolymer of tetrabromobisphenolsulfone (TBS) and BPA (Japanese Patent Application Laid-Open No. 123294/1976), (iii) a copolymer of tetrabromothiobisphenol (TBTDP) and BPA (Japanese Patent Application Laid-Open No. 99226/1981), (iv) a copolymer of the statistical mixture of halogenated bisphenols and BPA (Japanese Patent Application No. 136796/1976), and (v) a blend of the copolymer of thiobisphenol (TDP) and BPA and the copolymer of above (i) (Japanese Patent Application Laid-Open No. 50065/1979).

These copolymers are obtained by copolymerization of halogenated bisphenols resulted from halogen-substitution of benzene nucleus in bisphenols for the purpose of containing halogen in an amount necessary for a sufficient flame retardance. All of these copolymerization, however, require these halogenated bisphenols in a comparatively large amount, and accordingly, the mechanical strength of the resulting polycarbonate (particularly, impact resistance) is lowered.

Another example of halogen-containing polycarbonate is a polycarbonate in which halogenated phenol is used as the end terminator (Japanese Patent Publication No. 40715/1971). Said polycarbonate, however, is not provided with both of an excellent flame-retardance and a high mechanical-strength.

In order to overcome above disadvantages, a polycarbonate was produced by a process of copolymerizing BPA, TBA and TDP (Japanese Patent Application Laid-Open No. 140597/1977). According to said process, the resulting polycarbonate is excellent in both of flame retardance and mechanical strength, but it is not improved so much in moldability.

The present inventor's group proposed, as a novel polycarbonate being excellent in flame retardance, mechanical strength and other properties, a polycarbonate which is obtained by using pentahalogenophenol as an end terminator, and by copolymerizing BPA and TBA (Japanese Patent Application Nos. 79227/1989 and 79228/1989). Said polycarbonate, however, was found to have a few problems in thermostability at molding, although it is excellent in flame retardance and mechanical strength.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel polycarbonate which is excellent in both of flame retardance, and mechanical strength, and also in thermostability at molding.

Other objects and advantages of the present invention will become apparent from the following explanation.

According to the earnest investigation by the present inventors, it was found that the above objects are attained by the use of trihalogenophenol as the end terminator. The present invention has been accomplished on such a finding.

The present invention provides a polycarbonate

(1) having a repeating unit (I) represented by the general formula (A): ##STR3## wherein X¹ to X⁴ are each a halogen atom, and a repeating unit (II) represented by the general formula (B): ##STR4## (2) having, at the terminal thereof, a trihalogenophenoxy group or groups represented by the general formula (C): ##STR5## wherein X⁵ to X⁷ are each a halogen atom; and (3) having a viscosity average molecular weight of 10,000 to 50,000, and containing 1 to 10 mol % of the repeating unit (I) in the main chain.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an infrared absorption (IR) spectrum, by the thin film method, of the copolymer obtained in Example 1, and

FIG. 2 is a nuclear magnetic resonance (NMR) spectrum (solvent: deuteriochloroform) of said copolymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polycarbonate of the present invention has the repeating unit (I) represented by the general formula (A) mentioned above and the repeating unit (II) represented by the formula (B). Herein X¹ to X⁴ in the general formula (A) are each a halogen atom such as a bromine atom, a chlorine atom, and a fluorine atom. Said X¹ to X⁴ may be identical or different, but they are identical in most cases.

The polycarbonate of the present invention has a trihalogenophenoxy group or groups represented by the general formula (C) at the end, particularly both ends, of the molecules. X⁵ to X⁷ in said general formula (C) also indicate each a halogen atom such as a bromine atom, a chlorine atom, and a fluorine atom, as X¹ to X⁴ described above.

X¹ to X⁴ in the repeating unit (I) mentioned above may be identical to or different from X⁵ to X⁷ in the general formula (C).

In the polycarbonate of the present invention, the mole fraction of the repeating unit (1) based on the total of the repeating unit (I) and the repeating unit (II) in the main chain must be 0.01 to 0.1, preferably 0.02 to 0.06. If the mole fraction of the repeating unit (I) in the main chain is less than 0.01, the resulting polycarbonate has a lower flame retardance, while if it is in excess of 0.1, the mechanical strength of the resulting polycarbonate becomes poor.

As to the polymerization degree of the polycarbonate of the present invention, the viscosity average molecular weight is preferably in the range of 10,000 to 50,000. If the viscosity average molecular weight is less than 10,000, the mechanical strength such as impact resistance is insufficient.

The polycarbonate of the present invention has the abovementioned repeating units (I) and (II), and trihalogenophenoxy group or groups represented by the general formula (C) at the end thereof, and comprises a random copolymer, a block copolymer, or an alternating copolymer of them.

Said polycarbonate may contain a small amount of a repeating unit other than the above repeating units (I) and (II) in the molecular chain thereof. As the third copolymers to constitute these repeating units, bisphenol sulfone (BPS) or TDP is used. The content of them should be 0 to 20 mol %, preferably 0 to 10 mol % based on the total amount of BPA and TBA. If the content of it is in excess of 20 mol %, the mechanical strength of the resulting polycarbonate is poor.

The polycarbonate of the present invention can be produced in various methods. Preferred methods for producing them are following two.

According to the first method, an aqueous alkali solution (e.g., aqueous solution of sodium hydroxide, potassium hydroxide, and sodium carbonate) of tetrahalogenobisphenol A (e.g., tetrabromobisphenol A, tetrachlorobisphenol A, and tetrafluorobisphenol A) represented by the general formula: ##STR6## wherein X¹ of X⁴ are as defined before, an aqueous alkali solution of bisphenol A (BPA) represented by the formula: ##STR7## an aqueous alkali solution of trihalogenophenol (e.g., tribromophenol, trichlorophenol, and trifluorophenol) represented by the general formula: ##STR8## wherein X⁵ to X⁷ are as defined before are mixed with a solvent such as methylene chloride, chlorobenzene, pyridine, chloroform, and carbon tetrachloride, and a catalyst such as triethylamine and trimethylbenzylammonium chloride, in prescribed ratios and the resulting mixture is stirred. Then, phosgene is blown into the mixture to proceed with interfacial polycondensation. The reaction system is preferred to be cooled with water or ice since the reaction is exothermic. In this reaction, the reaction system becomes acidic as the reaction proceeds, so it is preferred to maintain pH at 10 or more by adding an alkali while measuring with a pH meter.

In the above reaction, a part (50 mol % or smaller) of trihalogenophenol can be replaced with a monohydric phenol such as p-tert-butylphenol and phenol, to be used in combination.

In the above polycondensation reaction, tetrahalogenobisphenol A of the formula (A') constitutes the repeating unit (I) of the resulting polycarbonate, and bisphenol A of the formula (B') constitutes the repeating unit (II), so the ratio of abovementioned tetrahalogenobisphenol A to bisphenol A to be placed is determined depending on the mole fraciton of each of the repeating units (I) and (II) of the polycarbonate to be produced, or the proportion of halogen atoms to be contained. On the other hand, the amounts of trihalogenophenol and phosgene introduced specify the polymerization degree of each of the repeating units (I) and (II), further the polymerization degree of the polycarbonate itself, and consequently the molecular weight thereof. Accordingly, the amounts of trihalogenophenol and phosgene to be introduced are determined depending upon the purpose of use. In blowing phosgene, the rate of phosgene to be blown per hour should be controlled so that a sufficient amount of phosgene might have been introduced at the completion of the reaction.

When the reaction product obtained in this way is introduced into a large amount of a precipitant such as methanol, then the polycarbonate of the present invention is precipitated out.

In the above reaction, various carbonate-forming compound derivatives such as bromophosgene, diphenyl carbonate, di-p-tolylcarbonate, phenyl-p-tolylcarbonate, di-p-chlorophenyl carbonate and dinaphtyl carbonate can be used in place of phosgene.

According to the second method, a polycarbonate oligomer is prepared in advance from bisphenol A and phosgene; the oligomer thus obtained, an aqueous alkali solution of tetrahalogenobisphenol A and an aqueous alkali solution of trihalogenophenol, a solvent such as methylene chloride which is capable of dissolving said oligomer, and further a catalyst such as triethylamine and trimethylbenzyl ammoniumchloride are mixed in prescribed ratios and stirred to be prepolymerized; and subsequently an aqueous alkali solution of bisphenol A and, if necessary, p-tert-butylphenol are added to proceed with polycondensation reaction. The resulting reaction product is poured into a large amount of a precipitant (e.g., methanol), and then the polycarbonate of the present invention is precipitated out.

The polycarbonate of the present invention can be efficiently produced by the abovementioned methods. In addition, also following methods are suitably used.

(i) Tetrahalogenobisphenol A and phosgene are reacted to prepare a polycarbonate oligomer in advance, and said oligomer is reacted with bisphenol A and trihalogenophenol in the presence of a solvent, an aqueous alkali solution, and a catalyst which are suitable for the reaction;

(ii) a polycarbonate oligomer prepared from bisphenol A (or tetrahalogenobisphenol A) and phosgene is reacted with tetrahalogenobisphenol A (or bisphenol A) and trihalogenophenol in the presence of a solvent, an aqueous alkali solution, a catalyst and so forth which are suitable for the reaction, and in that method, phosgene is blown in the reaction system;

(iii) an oligomer is prepared from bisphenol A and phosgene, and an oligomer is prepared from tetrahalogenobisphenol A and phosgene, and these two kinds of oligomers are reacted in the presence of trihalogenophenol and a solvent, an aqueous alkali solution, a catalyst and so forth which are suitable for the reaction; and

(iv) in the above method, a multi-stage polymerization, in which polymerization is carried out at two or more stages, is effectively employed.

The polycarbonate of the present invention can be obtained according to any of these methods.

The polycarbonate of the present invention has a viscosity average molecular weight of 10,000 to 50,000, preferably 13,000 to 50,000, as described above. In order to control the viscosity average molecular weight to be in that range, the amount of trihalogenophenol mainly used as the molecular weight controlling agent is appropriately regulated. Usually, the amount of trihalogenophenol is in the ratio of 0.01 to 0.1 (mole) based on the amount of diphenols which constitute the main chain.

In adding BPA, an aqueous alkali solution and catalyst such as triethylamine to polycarbonate oligomer, to produce polycarbonate by interfacial polycondensation, the ratio of catalyst to diphenols is usually 0.0005 to 0.03 (mol/mol).

The present invention also concerns a polycarbonate resin composition comprising (A) 100 parts by weight of the polycarbonate as defined above and (B) 1 to 10 parts by weight of a halogen-containing flame retarder.

As the halogen-containing flame retarder as Component (B), various ones can be used. Typical examples are (a) low-molecular weight polycarbonates comprising tetrahalogenobisphenol, (b) epoxy resins comprising tetrahalogenobisphenol, and (c) other flame retarders.

Among them, particularly preferred are those belonging to (a) and (b) above.

Herein above-mentioned (a) low-molecular weight polycarbonates comprising tetrahalogenobisphenol include low-molecular weight polycarbonates (polycarbonate oligomer) comprising m-times of the repeating units (x) represented by the general formula ##STR9## wherein X⁸ to X¹¹ are each a halogen atom, R is an alkylene group having 2 to 8 carbon atoms, an alkylidene group having 1 to 9 carbon atoms, a carbonyl group, a sulfone group, a sulfur atom or an oxygen atom, and n-times of repeating unit (y) represented by the general formula: ##STR10## wherein R' is an alkylene group having 2 to 8 carbon atoms, an alkylidene group having 1 to 9 carbon atoms, a carbonyl group, a sulfone group, a sulfur group atom or an oxygen atom, provided that m indicates an integer of 0 to 30, n indicates an integer of 0 to 30, and m+n=1 to 50 (particularly 3 to 20), and having a halogen content of 30% by weight. Herein, as the halogen-containing bisphenol compounds constituting the repeating unit (x), 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, bis(3,5-dibromo-4-hydroxyphenyl)methane, bis(3,5-dibromo-4-hydroxyphenyl)ether, bis(3,5-dibromo-4-hydroxyphenyl)sulfone and the like are used, and among them, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane (generally called Tetrabromobisphenol A) is particularly effective.

As the bisphenol compounds which constitute the repeating unit (y), 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)ether and the like are used, and among them, 2,2-bis(4-hydroxyphenyl)propane (generally called Bisphenol A) is particularly effective.

Next, (b) epoxy resins containing tetrahalogenobisphenol include polymers represented by the general formula: ##STR11## wherein, R¹ is an alkylene group having 2 to 8 carbon atoms, an alkylidene group having 1 to 9 carbon atoms, a carbonyl group, a sulfone group, a sulfur atom or an oxygen atom, R² is a hydrogen atom, a methyl group, an epoxypropyl group, a phenyl group, a 2-hydroxypropyl group or an oxygen atom, X¹² to X¹⁵ are each a halogen atom, and p is an integer of 1 to 30, and having a halogen content of 30% by weight or more.

Furthermore, (c) other flame retarders include tetrabromobenzene, tetrachlorobenzene, hexabromobenzene, hexachlorobenzene, hexabromobiphenyl, octabromobiphenyl, 2,2'-dichlorobiphenyl, 2,4'-dibromobiphenyl, 2,4'-dichlorobiphenyl, hexabromobiphenyl, triphenylchloride, tetrachlorophthalate, tetrachloroanhydride, tetrabromophthalate, tetrabromophthalic anhydride, tribromophenol and other known halogenated aromatic compounds; and diaromatic compounds such as 2,2-bis(3,5-dichlorophenyl)propane, bis(2-chlorophenyl)methane, bis(2,6-dibromophenyl)methane, 1,2-bis(2,6-dichlorophenyl)ethane, 1,1-bis(2-chloro-4-methylphenyl)ethane, 1,1-bis(3,5-dichlorophenyl)ethane, 2,2-bis(3-phenyl-4-bromophenyl)ethane, 2,3-bis(4,6-dichloronaphthyl)propane, 2,2-bis(2,6-dichlorophenyl)pentane, 2,2-bis(2,6-dichlorophenyl)hexane, bis(4-chlorophenyl)methane, bis(3,5-dichlorophenyl) cyclohexylmethane, bis(3-nitro-4-bromophenyl)ethane, bis(4-hydroxy-2,6-dichloro-3-methylphenyl)methane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 2,2-bis(3-bromo-4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane diglycydyl ether and the like. Further examples are halogenated diphenyl ethers, particularly preferable are those having 2 to 10 halogen atoms, such as decabromodiphenyl ether, octabromodiphenyl ether, hexabromodiphenyl ether, pentabromodiphenyl ether, tetrabromodiphenyl ether, tribromodiphenyl ether, dibromodiphenyl ether, hexachlorodiphenyl ether, pentachlorodiphenyl ether, tetrachlorodiphenyl ether, trichlorodiphenyl ether, dichlorodiphenyl ether and the like.

In the composition of the present invention, the halogen-containing flame retarder as Component (B) is blended in a ratio of 1 to 10 parts by weight, preferably 2.5 to 6 parts by weight based on 100 parts by weight of polycarbonate as Component (A). If the ratio of Component (B) is less than 1 part by weight, the resulting composition does not achieve a high flame retardance, while if it is in excess of 10 parts by weight, the mechanical strength of the composition becomes lower.

The composition of the present invention basically comprises the above components (A) and (B), but in addition to them, if necessary, various additives such as a resulting agent, stabilizer, lubricant, antioxidant, and ultraviolet absorbent can be added, so long as the transparency of the polycarbonate is not impaired.

When polycarbonate oligomer is added with BPA, an aqueous alkali and catalyst such as triethylamine, to produce a polycarbonate by interfacial polycondensation, the amount of caustic alkali is usually 0.1 to 5.0 to the amount of diphenols (mol/mol).

As described above, the polycarbonate of the present invention is excellent in flame-retardance, sufficiently high in impact resistance, and in addition, superior in thermostability at molding. More specifically, in this polycarbonate, flame retardance is V-O as an indication according to UL-94 (Underwriter's Laboratories Subject 94) (1/16 inch in thickness), Izod impact resistance as an indication of impact resistance is 40 kg cm/cm or more, and Yellowness Index (YI) after staying for 30 minutes at 300° C., as an indication of impact strength, is 20 or less.

Accordingly, the polycarbonate of the present invention is extensively and effectively used as various industrial materials such as materials for home electric appliances, office automation devices, or as construction materials, sheets, and so forth.

The present invention will be explained in greater detail with reference to the following examples.

PREPARATION EXAMPLE Preparation of Polycarbonate Oligomer of Bisphenol A

In a 2-liter flask equipped with a stirrer, 91 g of bisphenol A (BPA), 330 ml of methylene chloride and 560 ml of 2.0N aqueous solution of sodium hydroxide were placed, and stirred, and then phosgene was blown into the resulting mixture over 70 minutes while stirring and cooling on water bath. The reaction mixture was allowed to stand at room temperature, then a methylene chloride solution of oligomer was isolated as a lower layer. The oligomer has a concentration of 320 g/L (L=liter), a number average molecular weight of 850, and a concentration of the choloroformate group of 0.7 mol/L.

EXAMPLE 1

In a 50-liter reactor equipped with stirrer, 10 L of polycarbonate oligomer prepared in the above preparation Example, 1.8 L of an aqueous sodium hydroxide solution of tetrabromobisphenol A (TBA) and tribromophenol (TBP) (consisting of 250 g (0.460 mol) of TBA, 150 g (0.453 g) of TBP, 78.6 g (1.96 mol) of sodium hydroxide and 1.35 L of water) and 1.8 ml (0.013 mol) of triethylamine were placed in, and stirred at 500 rpm. After 60 minutes, 3.9 L of an aqueous sodium hydroxide solution of BPA (consisting of 457 g (2.00 mol) of BPA, 267 g (6.68 mol) of sodium hydroxide and 3.42 L of water) and 6.1 L of methylene chloride were added, and the resulting mixture was stirred.

After stirred for 60 minutes, the reaction product was separated into aqueous layer and ethylene chloride layer containing the copolymer formed.

This methylene chloride layer was washed with water, an acid (0.1N hydrochloric acid), ehtylene chloride was removed under reduced pressure at 40° C. to obtain a white powder of copolymer. This white copolymer was dried at 120° C. for one day and night, and then melted by the use of an extruder to be pelletized. The glass transition temperature (Tg) of the pellet was 152.6° C. The viscosity average molecular weight was 23,900, and the distribution of molecular weight was measured by the use of gel permeation chromatography, a distribution having a single peak at the abovementoned value was shown. An NMR analysis showed that the content of TBA (repeating unit (I)) in the main chain said copolymer was 3.1 mol %.

Then, said pellets were injection-molded at 300° C. and under the injection pressure of 55 kg/cm² in an injection molding machine. The test piece was measured for Izod impact strength and flame retardance. The flow value of the pellet was measured by a Koka-type flow tester.

The bromine content of the resulting pellet was 6.4% by weight. The bromine content was determined by alkali-decomposition of the sample, and analyzed by the Volhard method.

Further, the test on thermostability at molding was conducted as follows. The pellet was injection-molded to stay at 300° C. for 30 minutes, and then, test sample was formed. The resulting test piece was determined for yellowness index (YI) by the use of transmission-type photometer.

The results re shown in Table 1.

EXAMPLES 2 and 3

The procedure of Example 1 was repeated except that aqueous sodium hydroxide solution of TBA and TBP was changed as shown in Table 1. The results are shown in Table 2.

EXAMPLE 4

The procedure of Example 1 was repeated except that the aqueous sodium hydroxide solution of TBA and TBP was changed as shown in Table 1. The results are shown in Table 2.

EXAMPLE 5

The procedure of Example 1 was repeated except that the aqueous sodium hydroxide solution of TBA and TBP was changed as in Table 1. The results are shown in Table 2.

COMPARATIVE EXAMPLES 1 and 2

The procedure of Example 1 was repeated except that the amount of TBA in the aqueous sodium hydroxide solution of TBA and TBP was changed as in Table 1, and that p-tert-butylphenol (PTBP) was used in place of TBP. The results are shown in Table 2.

COMPARATIVE EXAMPLES 3

The procedure of Example 1 was repeated except that the aqueous sodium hydroxide solution of TBA and TBP was changed as shown in Table 1. The results are shown in Table 2.

COMPARATIVE EXAMPLES 4 and 5

The procedure of Example 1 was repeated except that the amount of TBA in the aqueous sodium hydroxide solution of TBA and TBP was changed as shown in Table 1, and that pentabromophenol (PBP) was used in place of TBP. The results are shown in Table 2.

                  TABLE 1                                                          ______________________________________                                                Content of Each Component in Aqueous Sodium                                    Hydroxide Solution of TBA and TBP (g)                                          TBA   BPS    TDP     TBP   PTBP   NaOH                                  ______________________________________                                         Example 1                                                                               250     --     --    150   --     78.6                                Example 2                                                                               391     --     --    150   --     102.4                               Example 3                                                                               247     --     --    179   --     85.0                                Example 4                                                                               180     74     --    179   --     109.2                               Example 5                                                                               180     --     161   179   --     162.3                               Comparative                                                                             444     --     --    --    81.1   78.6                                Example 1                                                                      Comparative                                                                             371     --     --    --    81.1   62.7                                Example 2                                                                      Comparative                                                                             895     --     --    150   --     187.6                               Example 3                                                                      Comparative                                                                             113     --     --    222   --     55.4                                Example 4                     (PBP)                                            Comparative                                                                             145     --     --    294   --     72.6                                Example 5                     (PBP)                                            ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________            Composition of     Whole Viscosity  Izod   Flame                               Copolymers in the                                                                          Composition                                                                           Content                                                                              Average                                                                              Flow Impact Retar-                                                                              Thermostability                Main Chain (mol %)                                                                         of TBP of Bromine                                                                           Molecular                                                                            Value*.sup.3                                                                        Resistance*.sup.4                                                                     dance*.sup.5                                                                        at Molding                     BPA                                                                               TBA                                                                               BPS                                                                               TDP                                                                               (mol %)                                                                               (wt %)*.sup.1                                                                        Weight*.sup.2                                                                        (ml/sec)                                                                            (kg cm/cm)                                                                            (1/16")                                                                             (YI)*.sup.6             __________________________________________________________________________     Example 1                                                                             96.9                                                                              3.1                                                                               0  0  3.0    6.4   23,900                                                                               2.4 ×                                                                         88     V-0   8                                                            10.sup.-2                                Example 2                                                                             95.1                                                                              4.9                                                                               0  0  2.9    8.4   23,700                                                                               2.6 ×                                                                         57     V-0   9                                                            10.sup.-2                                Example 3                                                                             96.7                                                                              3.3                                                                               0  0  3.8    7.3   19,300                                                                               6.3 ×                                                                         54     V-0  10                                                            10.sup.-2                                Example 4                                                                             95.5                                                                              2.4                                                                               2.1                                                                               0  3.9    6.4   19,300                                                                               5.6 ×                                                                         52     V-0  10                                                            10.sup.-2                                Example 5                                                                             92.3                                                                              2.5                                                                               0  5.2                                                                               3.8    6.5   19,700                                                                               5.9 ×                                                                         72     V-0   9                                                            10.sup.-2                                Comparative                                                                           94.5                                                                              5.5                                                                               0  0  0      6.5   19,900                                                                               6.2 ×                                                                         12     V-0   7                      Example 1                             10.sup.-2                                Comparative                                                                           95.4                                                                              4.6                                                                               0  0  0      5.5   20,800                                                                               5.9 ×                                                                         82     V-2   8                      Example 2                             10.sup.-2                                Comparative                                                                           88.9                                                                              11.1                                                                              0  0  3.0    15.5  22,100                                                                               2.1 ×                                                                         11     V-0  12                      Example 3                             10.sup.-2                                Comparative                                                                           98.6                                                                              1.4                                                                               0  0  3.1(PBP)                                                                              6.3   23,700                                                                               2.6 ×                                                                         90     V-0  29                      Example 4                             10.sup.-2                                Comparative                                                                           98.2                                                                              1.8                                                                               0  0  4.1(PBP)                                                                              8.2   18,100                                                                               2.2 ×                                                                         74     V-0  34                      Example 5                             10.sup.-2                                __________________________________________________________________________      *.sup.1 The bromine content derived from TBA and PBP in the whole              polycarbonate was calculated out. The amount of the bromine contained in       the polymer was determined by alkalidecomposting a sample and then by an       analysis according to the Volhard method.                                      *.sup.2 The viscosity average molecular weight (Mv) was determined by          calculation from a viscosity of a methylene chloride solution as measured      at 20° C. by the use of Ubbellohde viscometer.                          *.sup.3 The flow value was measured according to JIS K7210 (load: 160          kg/cm.sup.2).                                                                  *.sup.4 The Izod impact resistance was measured according to JIS K7110         using a test piece of 1/8 inch in thickness.                                   *.sup.5 the flame retardance was measured according to UL94 (Vertical          Combustion Test according to Underwriter's Laboratories Subject 94) using      a test piece of 1/16 inch in thickness.                                        *.sup.6 The thermostability at molding was determined by keeping the           injectionmolded pellet at 300° C. for 30 minutes, to form a test        piece, then the Yellowness Index (YI) of the test piece was judged by a        transmissiontype photometer.                                             

EXAMPLE 6

In a 50-liter reactor equipped with a stirrer, 10 L (L=liter) of polycarbonate oligomer solution prepared in the above Preparation Example, 1.8 L of aqueous sodium hydroxide solution of tetrabromobisphenol A (TBA) and tribromophenol (TBP) (consisting of 245 g (0.450 mol) of TBA, 150 g (0.453 mol) of TBP, 78.6 g (1.96 mol) of sodium hydroxide and 1.35 L of water), and 1.8 ml (0.013 mol) of triethylamine were placed, and stirred at 500 rpm. After 60 minutes, 3.9 L of an aqueous sodium hydroxide solution of BPA (consisting of 457 g (2.00 mol) of BPA, 267 g (6.68 mol) of sodium hydroxide, and 3.42 L of water) and 6.1 L of methylene chloride were added, and the resulting mixture was stirred. After being stirred for 60 minutes, the reaction product was separated into an aqueous layer and a methylene chloride layer containing the copolymer formed.

This methylene chloride layer was washed with water, an acid (0.1N hydrochloric acid), and water in that order, and then separated. From this methylene chloride layer, methylene chloride was removed under reduced pressure at 40° C. to obtain a white powder of copolymer (PC-1). This powder was dried at 120° C. for a whole day and night, and then melted by the use of an extruder, to be palletized. As the result of measuring the pellet, the glass transition temperature (Tg) of the pellet was 151.9° C.

The viscosity average molecular weight was 23,600, and when the distribution of molecular weight was measured by the use of gel permeation chromatography, a distribution having a single peak was shown. A NMR analysis showed that the contents of TBA and TBP in the main chain of said copolymer were 3.0 mol % and 3.0 mol %, respectively.

The resulting sample was alkali-decomposed, and the bromine content of the sample was determined to be 6.2% by weight according to the Volhard method.

EXAMPLE 7

In a 50-liter reactor equipped with a stirrer, 10 L of polycarbonate oligomer solution prepared in the above Preparation Example, 1.7 L of aqueous sodium hydroxide solution of TBA and TBP (consisting of 172 g (0.316 mol) of TBA, 180 g (0.544 mol) of TBP, 72.6 g (1.82 mol) of sodium hydroxide and 1.35 L of water) and 1.8 ml (0.013 mol) of triethylamine were placed, and stirred at 500 rpm.

After 60 minutes, 3.9 L of aqueous sodium hydroxide solution of BPA (consisting of 457 g (2.00 mol) of BPA, 267 g (6.68 mol) of sodium hydroxide and 3.4 L of water) and 6.1 L of methylene chloride were added, and the resulting mixture was stirred.

After being stirred for 60 minutes, the reaction produce was separated into an aqueous layer and a methylene chloride layer containing the copolymer formed.

This methylene chloride layer was washed with water, an acid (0.1N hydrochloric acid) and water in that order, and then separated. From this methylene chloride layer, methylene chloride was removed under reduced pressure at 40° C., to obtain a white powder of copolymer (PC-2).

Further, the powder was dried at 120° C. for a whole day and night, and then melted by the use of an extruder to be pelletized. As the result of measuring the pellet, its Tg was 150.8° C. The viscosity average molecular weight of said pellet was 19,800. A NMR analysis showed that the contents of TBA and TBP in the main chain of said copolymer were 2.1 mol % and 3.8 mol %, respectively.

The resulting sample was alkali-decomposed, and according to the Volhard method, the bromine content of the sample was found to be 6.0% by weight.

EXAMPLES 8 to 11 and COMPARATIVE EXAMPLES 6 to 9

After the polycarbonate prepared in Examples 6 and 7 and various halogen-containing flame retarders were dry-blended in the ratios shown in Table 3, the resulting blend was pelletized at 280° to 300° C by a uniaxial extruder having an inner diameter of 50 mm.

Subsequently, the pellet was injection-molded under an injection pressure of 55 kg/cm² to produce a test piece. Said test piece was measured for Izod impact resistance, flame retardance, and total light-transmittance.

The flow value of the pellet was measured by a Koka-type flow tester. The results are shown in Table 3.

                                      TABLE 3                                      __________________________________________________________________________                        Halogen-                                                           Poly- Poly- containing       Izod Impact      Total                            carbonate                                                                            carbonate                                                                            Flame Retarder                                                                           Flow Value*.sup.9                                                                     Resistance*.sup.10                                                                    Flame Retardance                                                                         Light-transmittance       No.    (PC-1)                                                                               (PC-2)                                                                               BC-52*.sup.7                                                                        EC-36*.sup.8                                                                        (ml/sec)                                                                              (kg/cm--cm)                                                                           1/16 inch                                                                           1/32 inch                                                                           (%)                       __________________________________________________________________________     Example 8                                                                             100    0    4.7  0    2.7 × 10.sup.-2                                                                 81     --   V-0  90                        Comparative                                                                           100    0    12   0    3.5 × 10.sup.-2                                                                 13     --   V-0  88                        Example 6                                                                      Example 9                                                                             100    0    0    4.4  2.9 × 10.sup.-2                                                                 83     --   V-0  90                        Comparative                                                                           100    0    0    12   4.2 × 10.sup.-2                                                                 11     --   V-0  89                        Example 7                                                                      Example 10                                                                             0    100   3.3  0    6.1 × 10.sup.-2                                                                 83     V-0  --   89                        Comparative                                                                            0    100   12   0    7.4 × 10.sup.-2                                                                 15     V-0  --   87                        Example 8                                                                      Example 11                                                                             0    100   0    3.0  6.3 ×  10.sup.-2                                                                84     V-0  --   90                        Comparative                                                                            0    100   0    12   7.9 × 10.sup.-2                                                                 11     V-0  --   88                        Example 9                                                                      __________________________________________________________________________      *.sup.7 Polycarbonate oligomer of tetrabromobisphenol A                        *.sup.8 Epoxy resin containing tetrabromobisphenol A                           *.sup.9 Measured according to JISK-7210 (Load: 160 kg/cm.sup.2)                *.sup.10 Measured according to JISK-7110 by the use of a sample piece of       1/8 inch in thickness.                                                         *.sup.11 Vertical Combustion Test was carried out according to                 Underwriter's Laboratories Subject 94 (UL94)                                   *.sup.12 Measured according to JISK-7105.                                 

What is claimed is:
 1. A polycarbonate comprising(1) a main chain comprising a repeating unit (I) represented by the formula: ##STR12## wherein X¹ to X⁴ are each a halogen atom, and a repeating unit (II) represented by the formula: ##STR13## (2) a trihalogenophenoxy group represented by the formula: ##STR14## wherein X⁵ to X⁷ are each a halogen atom, as the end group thereof; andsaid polycarbonate having a viscosity average molecular weight of 10,000 to 50,000, and the repeating unit (I) in the main chain is in a proportion of 1 to 10 mol %.
 2. The polycarbonate as defined in claim 1 wherein the trihalogenophenoxy group is a tribromophenoxy group.
 3. The polycarbonate as defined in claim 1 wherein the proportion of the repeating unit (I) in the main chain is 2 to 6 mol %.
 4. The polycarbonate as defined in claim 1 wherein X¹ to X⁴ are each a bromine atom.
 5. The polycarbonate as defined in claim 1, wherein X¹ to X⁷ are the same or different and are a halogen atom selected from the group consisting of bromine, chlorine and fluorine.
 6. The polycarbonate as defined in claim 2, wherein the proportion of the repeating unit (I) in the main chain is 2 to 6 mol %.
 7. The polycarbonate as defined in claim 2, wherein X¹ to X⁴ are each a bromine atom.
 8. The polycarbonate as defined in claim 3, wherein X¹ to X⁴ are each a bromine atom.
 9. The polycarbonate as defined in claim 6, wherein X¹ to X⁴ are each a bromine atom.
 10. The polycarbonate as defined in claim 9, wherein the viscosity average molecular weight is 13,000 to 50,000. 